The invention is directed to an oval-apertured, unevenly-spaced, three-turn coil with reflectors and shields, for depositing uniform heat in biological tissues at radiofrequencies.
Diathermy machines are known in the prior art, for instance as described by a patent and article of Ruggera et al.sup.1. The prior art coil described in the patent requires a four-to-one ratio of the length to the diameter for efficient (full-wave) uniform cross-sectional heating. A coil following this design and having a diameter of 60 cm would require a length of 240 cm (approximately 8 feet long). This was considered by clinicians to be a severe limitation, in that the whole body would have to be placed in the coil for treatment, thereby potentially heating unintended areas. Further, the longitudinal heating about the center of the coil's length occurs for approximately 30 cm out to the half-power points, and 60 cm is too large for most tumor treatments. Additionally the physical appearance and size of such a coil would present aesthetic and practical problems in a typical clinical setting. .sup.1 U.S. Pat. No. 4,527,550, "Helical Coil for Diathermy. Apparatus", issued 9 July 1985; and "Development of Family of RF Helical Coil Applicators which Produce Transversely Uniform Axially Distributed Heating in Cylindrical Fat-Muscle Phantoms", IEEE Transactions on Biomedical Engineering, Vol. BME-31, No. 1, Jan. 1984.